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Capacitive Touch Screen Data Processing
- May 10, 2018 -

After receiving the touch signal, the capacitive touch screen converts the touch data into an electrical pulse, which is transmitted to the touch screen control IC for processing. The signal is amplified by a low noise amplifier LNA and then converted and demodulated by the module, and finally sent to a DSP for data processing.

Capacitive touch screens generally have M+N(M column N rows) a physical capacitive touch sensor. The M+N interlaced sensors make up M*N capacitive sensing points, which change when the user's finger is close to the touch screen. The spacing between the sensors (that is, the distance between adjacent rows or columns) is usually around a few millimeters, and this distance determines the physical resolution of the touch screen M*N.

The coordinate system between the capacitive touchscreen module and the LCD module is completely different. The pixel coordinates of the LCD module are generally determined by its resolution. For example, a WVGA screen has a resolution of 800*480, which means 800 rows, 480 RGB pixels per row. Thus, a specific position can be determined by the pixel points (X, Y) in the X and Y directions. The capacitive touch screen module is based on the original physical dimensions of its X and Y directions. There must be a reasonable mapping method between the two coordinate systems to ensure the correctness of input and output operation.

So, touch screen control IC DSP processor to get data for capacitive touch screen pixel mapping transformation between the module and LCD module, to ensure that the induction to the user's touch the touch screen is referred to in the user.

In addition, in order to maintain the stability of touch coordinates and touch screen control IC need further processing of touch point jitter, including fingers shaking and capacitance data noise, according to the changes of the coordinates to change the filter coefficient of low pass filter, realize sitting mark smooth processing.

Finally, before uploading the data to the host, you have to use the software to analyze the data and determine what function each touch is intended to use. This process involves determining the size, shape, and location of the area being touched on the screen. If necessary, the processor will group the similar touches. If the user moves the finger, the processor calculates the difference between the starting point and the end point of the user's touch.


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